ES2888100T3 - Apparatus, systems and methods for obtaining information on electromagnetic energy emitted from the Earth, such as for locating a source of interference on Earth - Google Patents

Abstract

Satellite (10) to obtain information on electromagnetic energy emitted from a source (50) on Earth, or from sources on Earth, the satellite (10) orbiting the Earth in an orbit that has an inclination greater than 90º and less than 270º; and comprising the satellite (10): at least two reception antennas (11), each of the at least two reception antennas (11) has a reception pattern directed towards the Earth, and is suitable for receiving electromagnetic energy in a radio frequency range as the satellite (10) is orbiting relative to the Earth's surface, and the at least two receiving antennas (11) forming overlapping but not identical receiving patterns; and a transmitter configured for at least one of the following three operations: retransmit at least part of the received electromagnetic energy; transmit information representing at least part of the received electromagnetic energy; and transmitting information that is derived from at least part of the received electromagnetic energy.

Description

DESCRIPTION

Apparatus, systems and methods for obtaining information on electromagnetic energy emitted from the Earth, such as for locating a source of interference on Earth

[Tech field]

The present invention especially relates to telecommunications and to obtaining information on electromagnetic energy emitted from a source or sources on Earth. The invention can be used, for example, to locate a source of interference on Earth, although the invention is not limited to this particular application.

[Background]

Satellite communications especially involve the transmission of signals from a station on Earth to a satellite and vice versa. Satellite communications may be intended to provide communication services between two points on Earth. This includes point-to-point services (eg Internet, satellite phones) and point-to-multipoint (broadcast) services (eg TV). The stations taking part in satellite communications may be fixed (eg, rooftop satellite dish) or mobile (eg, vehicles, ships, aircraft, handheld devices). With the increased use of satellite and terrestrial communications, the risk of interference between different communications also increases.

In the past, there have been numerous efforts to locate interfering transmission stations and, more generally, there have been numerous efforts to resolve interference problems and to alleviate the disruptions caused by them (including reducing the usable capacity of a transmission system). satellite communication).

A known approach to locating an interfering transmitting station on Earth is to use ground stations. For example, US 5,008,679 relates to a method of locating an unknown radio frequency transmitter using correlations between signals received by different satellites. However, performing ground-based geolocation is difficult because it relies on signal correlation between multiple satellites and multiple ground stations: a time-consuming process with many opportunities for error propagation within the calculation. In addition, the ability to perform ground-based geolocation depends on many factors, including the existence of and extensive knowledge of adjacent satellites, the existence of and extensive knowledge of known reference signals, and the existence of necessary ground hardware and, as As a result, ground-based geolocation is ineffective in many cases.

Another known approach uses helicopters or unmanned aerial vehicles (UAV) for geolocation. However, this approach is an inefficient resource and only offers point analysis.

The prior art further includes:

- JP 2004-328088, which refers to a monitoring satellite in a retrograde orbit, which picks up the signals transmitted to a geostationary satellite and sends them to a ground station using a different frequency than the one used for transmission from the Earth to the satellite. The purpose is to determine the position of an interference source on Earth.

- document US 6,147,640, which relates to an interference location system for determining the location of an interference signal received by a communication satellite. The communication satellite has an "Earth-facing panel" on which an array of antennas is located.

In view of the above, there is a need to reduce the amount of interference in the context of satellite communications or, when this is not possible, to adopt techniques to deal with such interference.

[Summary]

In order to meet or at least partially meet the aforementioned need, apparatus, systems and methods according to the invention are defined in the independent claims. Particular embodiments are defined in the dependent claims and explained in the present description.

In one embodiment, a satellite, hereinafter referred to as an "observing satellite", is used to obtain information on electromagnetic energy emitted from a source or sources on Earth. The observation satellite orbits the Earth in an orbit that has an inclination greater than 90° (that is, 90 degrees) and less than 270° (that is, 270 degrees), defining such an orbit as retrograde to the direction of rotation. nature of the Earth. Furthermore, the observation satellite comprises at least one receiving antenna and one transmitter. The at least one receiving antenna has a receiving pattern directed towards the Earth, and is suitable to receive electromagnetic energy in the radio frequency range as the observation satellite is orbiting relative to the Earth's surface. The transmitter is configured to at least one of: (i) retransmit at least part of the received electromagnetic energy, (ii) transmit information representing at least part of the received electromagnetic energy, and (iii) transmit information that is derived from at least least part of the received electromagnetic energy.

Therefore, the observation satellite is capable of collecting data that significantly improves the ability to understand the composition and origin of the energy transmitted to space for the purposes of satellite communications. Since most communication satellites are designed for communications rather than data collection or analysis functions, an observation satellite can provide radically more data, which cannot be collected by communication satellites as they exist today. , on the nature of uplink transmissions. Interference detection, system optimization, spectrum planning, and many other applications greatly benefit from the data and insights produced by the observation satellite. In particular, by placing the observation satellite in a highly inclined (retrograde) orbit, its velocity relative to the Earth's surface is greater than that of a satellite in a prograde orbit at a similar altitude, and the observation satellite is capable of frequently revisit a given position with respect to the Earth's surface and receive transmissions from a given area on Earth. Furthermore, in one embodiment, placing the observation satellite at an altitude similar to the altitude of satellites to which transmissions of interest are generally intended (hereinafter referred to as "target satellites") is advantageous because the observation satellite observation can then be able to observe a large area on Earth and observe most of the signals destined for certain target satellites.

The use of the observation satellite mentioned above to understand and manage interference problems in the context of satellite communications results from a change in focus. The purpose is to try to discover what signals are being emitted into space from sources on Earth. However, instead of trying to do this from a point near the Earth's surface, the observation satellite allows this to be done from a point in space and especially from a point near the orbit of interest. Therefore, this allows information on signals reaching the orbit of interest to be collected more efficiently.

Inclination is the angle between the equatorial plane and the plane in which the satellite orbits the Earth. A satellite with an inclination of 0° (ie 0 degrees) is defined as orbiting in the equatorial plane in the direction of the Earth's rotation.

As mentioned above, the observation satellite transmitter is configured to perform one of three operations (denoted (i), (ii) and (iii) respectively), a combination of two of these three operations (namely, (i) +(ii), (i)+(iii), or (ii)+(iii)), or all three operations (specifically, (i)+(ii)+(iii)).

Specifically, in a sub-embodiment, the transmitter is configured to retransmit at least part of the received electromagnetic energy (eg, to a ground station on Earth, or to another satellite). Therefore, the received electromagnetic energy, or a part of it, can be transmitted without any processing by the observation satellite itself. In that case, any processing of the received electromagnetic energy, or a part of it, (for analysis, geolocation, etc.) can then be done outside the observation satellite, for example on Earth, by means of a processing station.

Alternatively or additionally, in another sub-embodiment, the transmitter may be configured to transmit (eg to a ground station on Earth, or to another satellite) information representing at least part of the received electromagnetic energy. This may mean, for example, digitizing and/or compressing the received electromagnetic energy, or a part of it.

Alternatively or additionally, in yet another sub-embodiment, the transmitter may be configured to transmit (eg, to a ground station on Earth, or to another satellite) information that is derived from at least part of the received electromagnetic energy (especially instead of of the received electromagnetic energy itself). The information may be derived from the received electromagnetic energy, or a part thereof, for example by determining or estimating, using some equipment (also called a "payload") within the satellite itself, the location on Earth of the source of received electromagnetic energy (such as the source of an interference source). Deriving information from the received electromagnetic energy, or a part thereof, may also comprise generating, using some equipment within the satellite itself, information about the energy spectrum, polarization, modulation scheme, etc. of the received electromagnetic energy.

In other words, the observation satellite is used to obtain information on electromagnetic energy emitted from a source, or sources, on Earth in the sense that the process of actually obtaining the information on received electromagnetic energy can be done within or outside the observation satellite. Specifically, the observation satellite can act as a tool that contributes to the process of obtaining information on electromagnetic energy emitted from a source, or sources, on Earth.

In one embodiment, the observation satellite is suitable for obtaining information on electromagnetic energy emitted from a source, or sources, on Earth and reaching geostationary orbit. Monitoring signals transmitted to satellites in the geostationary orbital arc at an altitude of approximately 35,800 km is particularly interesting since the geostationary orbit is of paramount importance for numerous satellite communications.

In one embodiment, the observation satellite transmitter is configured to transmit, toward Earth, at least part of the received electromagnetic energy or information representing, or derived from, at least part of the received electromagnetic energy. Doing this allows a receiving station on Earth, or a processing station communicating with such a receiving station, to derive additional information from the electromagnetic energy received by the satellite. For example, the location of the source of any received electromagnetic energy can be determined.

However, the transmitter may not be configured to directly send received electromagnetic energy (or a portion thereof) or information representing, or derived from, received electromagnetic energy toward Earth. Instead, another satellite or space vehicle can function as a transmitting station that relays the transmission to Earth. Such a transmitting satellite or spacecraft may be configured to perform further processing of information received from the observation satellite.

In one embodiment, the information derived from the received electromagnetic energy is obtained by processing at least part of the received electromagnetic energy within the observation satellite. In such a case, the processing equipment is integrated with the observation satellite to do this.

In one embodiment, the processing comprises at least one of: (a) selectable downconversion of analog signal to common intermediate frequency; (b) analog to digital conversion of signals provided by, ie carried by, at least part of the received electromagnetic energy; (c) spectrum analysis of at least part of the received electromagnetic energy; (d) Doppler shift analysis of at least part of the received electromagnetic energy; (e) Doppler rate analysis of at least part of the received electromagnetic energy; (f) arrival direction or arrival angle processing; (g) time difference of arrival (TDOA) processing; (h) frequency difference of arrival (FDOA) processing; (i) reference measurements between two or more antenna elements; (j) data filtering; and (k) data compression.

Therefore, the observation satellite may be able to perform different types of processing on the received electromagnetic energy.

For example, through analog-to-digital conversion, signals carried by received electromagnetic energy become accessible for further digital processing.

Spectrum analysis and direction-of-arrival (or direction finding (DF)) processing can also help identify the composition and origin of electromagnetic energy, respectively. One skilled in the art would know how to perform spectrum analysis and direction of arrival (DOA) processing. In that regard, more background on DOA processing can be found, for example, in Schmidt, RO, “Multiple emitter location and signal parameter estimation,” IEEE Transactions on Antennas and Propagation, Vol. 34, No. 3, 276- 280, March, 1986; or in Lipsky, Stephen E., “Microwave passive direction finding”, SciTech Publishing, 2003. There are numerous other references in the academic literature on direction of arrival processing.

Data filtering and data compression could reduce the amount of data transmitted by the observation satellite.

In one embodiment, the at least one observation satellite receiving antenna is suitable for receiving electromagnetic energy in a radio frequency range between 1 GHz and 100 GHz. Obtain, and then analyze, electromagnetic energy in the microwave range (i.e. , between 1 GHz and 100 GHz) is particularly advantageous since satellite communications are generally performed in this range so that interference in the context of satellite communications is mainly caused by electromagnetic energy in this frequency range.

In a sub-embodiment of the aforementioned embodiment, the at least one receiving antenna of the observation satellite is suitable for receiving electromagnetic energy in a radio frequency range that is at least one of: (a) between 1 and 2 GHz (L-band) ; (b) between 2 and 4 GHz (S band); (c) between 4 and 8 GHz (C band); (d) between 8 and 12 GHz (X-band); (e) between 12 and 18 GHz (K ^u band); and (f) between 26.5 and 40 g Hz (K ^a band). These exemplary frequency bands are of particular interest for satellite communications.

In one embodiment, the at least one observation satellite receiving antenna is suitable for receiving electromagnetic energy in a radio frequency range used by geostationary satellites to receive signals from Earth. In other words, the observation satellite can be used to obtain information on electromagnetic energy emitted from the Earth for the purpose of satellite communications regardless of radio frequency.

In one embodiment, the at least one observation satellite receiving antenna is suitable for receiving electromagnetic energy having at least one of: a linear polarization; a vertical polarization; a horizontal polarization; an elliptical polarization; and a circular polarization. This embodiment is advantageous since it can be useful to obtain information about the polarization of the received electromagnetic energy.

In one embodiment, the at least one receiving antenna of the observation satellite is configured to receive, during an orbital period, electromagnetic energy from an area that covers more than half of the Earth's surface.

In one embodiment, the received electromagnetic energy comprises more than just information intended to control the observation satellite itself. The purpose of the observation satellite is, in fact, to collect information on signals destined for satellites other than the observation satellite. The observation satellite is intended to collect information on signals destined for so-called target satellites, as mentioned above.

In one embodiment, the received electromagnetic energy comprises energy intended for at least one other satellite. The signals to control the observation satellite itself can be transmitted in a specific frequency band, or through other means as will be explained below. Therefore, in this embodiment, the electromagnetic energy received by the observation satellite is not a control signal for the observation satellite.

In one embodiment, the observation satellite orbits the Earth in an orbit having an inclination greater than 175° (175 degrees) and less than 185° (185 degrees). In such an orbit, the observation satellite moves in an orbit particularly advantageous for receiving electromagnetic energy transmitted in the direction of the geostationary orbit.

In one embodiment, the observation satellite orbits the Earth in an orbit having an apogee that differs by no more than 4000 kilometers from the geostationary orbit. In this orbit, the observation satellite is capable of receiving electromagnetic energy that closely corresponds to the actual electromagnetic energy reaching the geostationary orbit. This therefore allows the observation satellite to obtain data to provide a good estimate of the actual electromagnetic energy reaching geostationary satellites.

In one embodiment, the observation satellite orbits the Earth in an orbit having an apogee that is any one of: between 31,700 and 34,700 kilometers above mean sea level, and between 36,700 and 39,700 kilometers above mean sea level. In this orbit, the risk of collision with the geostationary satellites themselves and other resident space objects (RSOs), including space debris, is further minimized, based on the current public catalog of orbiting objects.

In one embodiment, the observation satellite orbits the Earth in an orbit that has an eccentricity that is less than 0.05.

In one embodiment, the observation satellite is not itself a communication satellite for transmitting end-user information from one point on Earth to another point on Earth. Therefore, in this embodiment, the observation satellite operates independently of existing communication satellites. The observing satellite, as an independent entity, therefore also provides the ability to monitor spectrum between existing geostationary satellites, at vacant orbital locations along the arc. This allows assessment of the spectrum environment prior to deploying a satellite asset to a given location, which could inform spectrum planning and fleet deployment decisions. This shows that, in some embodiments, the observation satellite can be used beyond interference management.

In one embodiment, the observation satellite transmitter is configured to transmit (or retransmit) using at least one of: (a) downlinking the data (i.e., the data corresponding to the aforementioned cases (i), (ii) or (iii), or any combination thereof) through the use of specific dedicated microwave frequencies; (b) perform a data downlink using a transmitter capable of dynamically adjusting its transmission frequency band; (c) transmission using low level spread spectrum; (d) at least one optical communication link; and (e) a store-and-forward method in which the transmission (or retransmission) is delayed from the reception of the signal.

In one embodiment, the satellite further comprises a receiver connected to at least one receiving antenna, the receiver having sufficient spectrum capacity and agility to reconfigure to different frequencies over a wide range of the radio frequency spectrum. Therefore, the satellite can receive electromagnetic energy in a wide frequency range as opposed to existing satellites.

The invention also relates to a satellite for obtaining information on electromagnetic energy emitted from a source or sources on Earth. The satellite orbits the Earth in an orbit that has an inclination greater than 90° (ie 90 degrees) and less than 270° (ie 270 degrees). The satellite comprises means for receiving, while that the satellite is orbiting with respect to the surface of the Earth, electromagnetic energy in the radio frequency range, from a source, or sources, on Earth using at least one receiving antenna having a receiving pattern directed towards the Earth. The satellite also comprises transmission means for at least one of: (i) retransmitting at least part of the received electromagnetic energy; (ii) transmit information representing at least part of the received electromagnetic energy; and (iii) transmitting information that is derived from at least part of the received electromagnetic energy.

In one embodiment, a plurality of satellites as described above are used together in order to obtain information on electromagnetic energy emitted from a source or sources on Earth.

The invention also relates to a method of operating a satellite, or a plurality of satellites, as described above.

The invention also relates to a system comprising at least one observation satellite according to any one of the above embodiments, at least one ground station configured to obtain, from the at least one observation satellite, the electromagnetic energy received or the information representing, or derived from, the received electromagnetic energy, and at least one processing station. The at least one processing station is configured to estimate, from the received electromagnetic energy or the information that represents, or is derived from, the received electromagnetic energy, obtained by the at least one ground station, at least one of : (a) the composition of at least part of the received electromagnetic energy; (b) a location on Earth of the origin of at least some of the received electromagnetic energy; (c) a level of received electromagnetic energy that reaches at least part of the geostationary orbit; and (d) at least one characteristic of an uplink transmission.

In the system described above, the processing station is located on Earth. However, the invention is not limited to such a configuration. As explained above, the processing can also be carried out, for example, completely or partially on the observation satellite or on another satellite.

When more than one observation satellite is used, the amount of electromagnetic energy received can be increased. In addition, the response time, ie the time from when an action is requested from the system to the corresponding response, can be reduced.

The invention also relates to a method comprising: obtaining, by means of at least one ground station, a signal originating from a satellite (in this case called "observation satellite", as mentioned above) orbiting Earth in an orbit that has an inclination greater than 90° (90 degrees) and less than 270° (270 degrees). The signal communicates at least one of: (i) electromagnetic energy received by the observation satellite, (ii) information representing electromagnetic energy received by the observation satellite, and (iii) information that is derived from electromagnetic energy received by the satellite observational. The method also comprises: estimating, by means of at least one processing station, from at least part of the received electromagnetic energy or the information that represents, or is derived from, at least part of the received electromagnetic energy, obtained by means of the at least one ground station, at least one of: (a) the composition of at least part of the received electromagnetic energy; (b) a location on Earth of the origin of at least some of the received electromagnetic energy; (c) a level of received electromagnetic energy that reaches at least part of the geostationary orbit; and (d) at least one characteristic of an uplink transmission.

In the context of the method described above, the processing station is located on Earth. However, as already mentioned above, the invention is not limited to such a configuration. The processing can also be carried out, for example, completely or partially on the observation satellite or on another satellite.

In one embodiment, estimating the location comprises estimating a longitude and latitude. In such a manner, the location of the origin (ie, source) of the electromagnetic energy can be determined. Determining the source of the electromagnetic energy may then allow the interference to be removed, for example by a satellite operator contacting a transmission station operator to stop transmission or by a transmission station operator carrying out repairs. necessary from damaged or misaligned equipment.

In one embodiment, estimating a location on Earth of the origin of at least part of the received electromagnetic energy comprises estimating the location of an interfering source.

In one embodiment, estimating at least one characteristic of an uplink transmission comprises estimating an uplink pattern of at least one of an antenna on Earth and a group of antennas on Earth.

The invention also relates to a method of operating an observation satellite, to the use of an observation satellite for the aforementioned purposes (i.e., to estimate: (a) the composition of at least part of the received electromagnetic energy; (b) a location on Earth of the origin of at least part of the received electromagnetic energy; (c) a level of received electromagnetic energy that reaches at least part of the geostationary orbit; and (d) at least one characteristic of a transmission uplink).

[Brief description of the drawings]

Embodiments of the present invention will now be described, together with the accompanying figures, in which:

Figure 1 schematically illustrates an exemplary situation in which a satellite experiences interference; Figure 2 schematically illustrates another exemplary situation in which a satellite experiences interference; Figure 3 schematically illustrates an exemplary situation where the operation of a satellite is disturbed by a ground station picking up a terrestrial transmission;

Figure 4 schematically illustrates an observation satellite in a retrograde orbit and another satellite, in an embodiment of the invention;

Figure 5 schematically illustrates an observation satellite in a retrograde orbit and another satellite, in an embodiment of the invention;

Figure 6 schematically illustrates a highly inclined satellite, ie in a retrograde orbit, in one embodiment of the invention;

Figure 7 schematically illustrates the composition of an observation satellite in an embodiment of the invention; Figure 8 schematically illustrates the composition of an observation satellite payload in one embodiment of the invention;

Figure 9 schematically illustrates a composition of a processing station in an embodiment of the invention;

Figure 10 schematically illustrates a transmission from a satellite through a transmission element; Figure 11 schematically illustrates a method in one embodiment of the invention; Y

Figure 12 schematically illustrates a method in one embodiment of the invention.

[Detailed description]

The present invention will now be described in conjunction with specific embodiments. The specific embodiments serve to provide those skilled in the art with a better understanding, but are not intended in any way to restrict the scope of the invention, which is defined by the appended claims. In particular, the embodiments described independently throughout the description may be combined to form additional embodiments to the extent that they are not mutually exclusive.

Figure 1 schematically illustrates a satellite 30 orbiting the Earth in a geostationary orbit (referred to as "GEOorbit" in Figure 1), in order to understand the problems addressed by some embodiments of the invention. Satellite 30 receives an uplink signal (referred to as "uplink" in Figure 1) from a ground station 60 (eg, audio or data to be transmitted to another point on Earth). Additionally, another ground station 50 transmits electromagnetic energy (referred to as the "interfering carrier" in Figure 1) toward the location of the satellite 30 due to, for example, a misdirected satellite dish (i.e., mispointed antenna) or because the pattern of radiation from the ground station 50 antenna does not serve to direct it sufficiently (for example, because its main lobe is too wide, because a side lobe is incidentally in the direction of satellite 30, or because the transmit power is too low). too high). The electromagnetic energy transmitted from the ground station 50 may be destined for an adjacent satellite but partially reaches the satellite 30. The electromagnetic energy transmitted from the ground station 50 appears as interference to the geostationary satellite 30. The interference can disturb the normal operation of the satellite 30, for example, by reducing the usable capacity of the satellite link, for example, in terms of data throughput, usable bandwidth, usable power at a given transponder, threshold stability minimum noise, etc. In Figure 1, the distance between the orbit of satellite 30 (illustrated by the dashed line) and the curvature of the Earth's surface (illustrated by the solid line) are schematic and not to scale. Also, the satellite and ground stations depicted are also not to scale. These remarks also apply to figures 2, 3, 4, 5, 6 and 10.

Figure 2 schematically illustrates another situation in which the satellite 30 experiences interference, in order to understand the problems addressed by some embodiments of the invention.

In this case, a ground station 60 transmits an uplink signal to a satellite 31 that is in a lower orbit than satellite 30. For example, satellite 31 is in Low Earth Orbit (LEO) or High Earth Orbit. Middle Earth (MEO) and satellite 30 is in a geostationary orbit. Although the uplink signal is not destined for satellite 30, the electromagnetic energy carried by the uplink signal reaches satellite 30 since, at least at one point in time, satellites 30, 31 are on the same line of sight. view seen from station 60 on the ground. Therefore, the satellite 30 may experience interference. The same problem can occur when satellite 31 is moving in a higher orbit compared to satellite 30. Such a situation is explained for example in Thomas J. Lang, “Conjunction / Interference Between LEO and GEO Comsats”, Proceedings of the AAS/A iaA Astrodynamics Specialist Conference held in Sun Valley, Idaho, August 4-7, 1997, AAS Paper 97-668.

Figure 3 schematically illustrates another situation in which the operation of a satellite may be disturbed, in order to further understand the problems addressed by some embodiments of the invention.

A base station 61, for example, used in a mobile communication system, broadcasts a signal to mobile devices or other base stations. This transmission is incidentally picked up by a station 60 on the ground. In other words, ground station 60 accidentally includes the transmission in an uplink sent to satellite 30. Therefore, satellite 30 receives electromagnetic energy that comprises not only an uplink signal for satellite 30 but also a non-uplink signal. destined for satellite 30.

The occurrence of this type of interference phenomenon has been recognized by spectrogram analysis. Indeed, it has been shown in the past that, for example, GSM rebroadcasting can occur as evidenced by spectrogram analysis clearly showing timing correction bursts. In GSM, in fact, a burst of timings is sent after every tenth frame. Since each GSM frame is 4.615 ms, the timing burst every 46.15 ms has been observed. This situation may occur in some circumstances for example if a mobile communication cell tower (base station) is close to a VSAT uplink antenna (such as a few hundred meters from each other). The VSAT uplink antenna is then capable of capturing and retransmitting signals from the mobile communication cell tower to the geostationary orbit.

Now that some exemplary interference situations have been explained with reference to Figs. 1 to 3, embodiments of the invention will be described in more detail.

In one embodiment, an observation satellite 10 is used to obtain information about the electromagnetic energy reaching a satellite 30 (which is, for example, a geostationary satellite) or, more generally, reaching an orbit or group of orbits. In this regard, Figure 4 schematically illustrates an observation satellite 10 in a retrograde orbit (although several observation satellites 10 may also be used), a ground station 20 receiving transmissions from and transmitting control signals to the observation satellite 10 , a processing station 40 that processes received transmissions, a satellite 30 in a geostationary orbit, a transmit station 60 that transmits an uplink signal to satellite 30, and a transmit station 50 that incidentally transmits electromagnetic energy to the satellite 30. In the example shown in Figure 4, the satellite 30 is assumed to be in a geostationary orbit, although the invention is not limited to this situation.

The observation satellite 10, which orbits the Earth in a retrograde orbit, is capable of receiving the transmissions from the stations 50, 60 on the ground. Furthermore, the observation satellite 10 sends information about the received electromagnetic energy to a station 20 on the ground. The information is then used in a processing station 40 to process, for example, to derive various types of information. For example, processing station 40 may determine the location of interfering ground station 50 so that it can adjust ground station 50's parabolic antenna or so that satellite 30's antenna reception pattern can be adapted to avoid receiving interference. unwanted signals from the ground station 50 (eg, by generating nulls in the direction of the interfering ground station 50).

Figure 5 schematically illustrates a configuration in which the observation satellite 10 orbits at an altitude higher than the geostationary orbit, rather than lower than the geostationary orbit. Furthermore, the configuration illustrated by Figure 5 is similar to that illustrated by Figure 4.

The advantages of using a retrograde orbit for the observation satellite 10 will now be explained in more detail.

retrograde orbit

To achieve maximum value from a satellite with spectrum detection capabilities (ie, an observation satellite), some embodiments of the present invention extend the detection coverage to as many satellites as possible. Typically, movement of a satellite relative to other satellites in a given orbit requires expending fuel, resulting in shortened lifespan, increased spacecraft cost, or slow relative drift speed. Theoretically it could be orbited very quickly with respect to other satellites at the appropriate altitude if the satellite had to continuously burn fuel. However, this is not practical and probably not even feasible with current technology. Therefore, the rate of drift possible, while also maintaining the vantage point altitude, would be at such a slow rate as to limit the value of the system extremely. Although a slow drift rate may fit more strategic value-added needs, since fleet deployment and spectrum development work on long timescales, a slow drift rate also precludes them as a suitable operational monitoring platform. for sensitivity to active communications transmissions since it could take months to redeploy the asset to the required orbital location. For this reason and to maximize the number of satellites served, the proposed solution is for the observation satellite 10 to operate in an alternative retrograde orbit at a near geosynchronous altitude, which orbits the Earth against the natural rotation about its axis. In this case, a retrograde orbit is understood to be an orbit that has an inclination greater than 90° and less than 270°.

The use of satellites orbiting in a retrograde orbit is known, but for other applications and configurations. For example, US 2008/0081556 A1 refers to placing a satellite in a retrograde orbit for observation and inspection satellites.

Preferably, the inclination of the retrograde orbit is between 175° and 185° so that the observation satellite 10 moves close to the equatorial plane. A further schematic illustration of a retrograde orbit is shown in Figure 6. This orbit has the advantage of continuous and natural motion relative to geosynchronous satellites and provides a reasonable flyby frequency for each geosynchronous spacecraft of interest. The retrograde orbit allows measurement at the appropriate altitude without the need to spend significant fuel. More specifically, retrograde orbit allows the desired revisit rate and strategic position as a natural movement so that only the necessary fuel is required to achieve and maintain orbit over the lifetime of the satellite (similar to all other satellites). The altitude is preferably similar to geostationary satellites, plus or minus up to several thousand kilometers in order to provide a safety margin for conjunction with other satellites at that altitude. Altitude is significant to the detection operations of the observation satellite 10 because being at a similar height allows the observation satellite 10 to monitor the same transmissions, or nearly the same transmissions, that the geostationary satellites 30 receive. If the spacecraft's altitude were too high or too low, some transmission signals (from antennas with low elevation angles on Earth) would potentially be lost and unwanted microwave energy potentially received.

In case the altitude of the observation satellite 10 is approximately the same as the geostationary satellites 30, that is, the observation satellite 10 for example orbits the Earth in an orbit having an altitude that differs by no more than 4000 kilometers from geostationary orbit, the orbital period is still approximately one satellite rotation every twenty-four hours. However, since the rotation of the Earth and the geostationary satellite orbit would be equal in magnitude but opposite in direction, the observation satellite 10 passes each geostationary satellite 30 approximately twice every twenty-four hours. The orbit can also be described as a prograde geosynchronous type with an inclination of 180 degrees. The fast arrival rate at each geostationary satellite 30 and the extensive coverage over the entire arc therefore makes a single observation satellite 10, with its microwave detection capabilities, capable of servicing an entire fleet.

Since a retrograde orbit is not useful in a traditional geosynchronous satellite communications sense, few retrograde launches have been made. Additional energy is required to launch a retrograde satellite from the Earth's surface since the momentum provided by the Earth's natural rotation has to be reversed to achieve an orbit in the opposite direction.

The most direct launch approach is to launch west from the Earth's surface, accounting for additional thrust to achieve the necessary delta-v in the retrograde direction. However, since most launches are prograde, launch sites are located based on favorable eastward launch conditions (a large body of water directly to the east). An additional approach is a more traditional eastward launch into a supersynchronous transfer orbit and uses propulsion onboard the spacecraft to increase the tilt to 180 degrees over time. However, such launches should not be viewed as the only means of achieving such an orbit.

Another launch approach is to use the moon to deflect by the lunar gravitational pull and 'reverse' the Earth's rotation, as explained for example in Aravind, R., et al, “Mission to Retrograde Geo-equatorial Orbit (RGEO) using lunar swing-by”, 2012 EEE Aerospace Conference (March 3-10, 2012), pp. 1-8.

Satellite Composition

Figure 7 schematically illustrates the composition of an observation satellite 10 in an embodiment of the invention. Observation satellite 10 and its equipment can be built on top of an existing spacebus, including power, propulsion, control, thermal, and other subsystems. Specialized payload (i.e. equipment) could comprise the following important subsystem components: groupings 11 only for receiving and control components 12 (control unit) necessary to enable space-based geolocation, spectrum processing and analysis hardware, a communications subsystem 13 (referred to as "COM" in Figure 7) to receive commands from the ground and download processed data (temporary storage data for transmission if necessary) and telemetry, and a propulsion system 14 . The propulsion subsystem is specifically depicted due to the significance of this subsystem in achieving the prescribed orbit, depending on the launch method. However, observation satellite 10 may not contain all of the aforementioned subsystems and could contain additional subsystems in other embodiments.

The antenna 11 has a reception pattern directed towards the Earth and is suitable for receiving electromagnetic energy in the radio frequency range. The received electromagnetic transmission may comprise an intentionally transmitted signal and/or noise-like transmissions. Preferably, the antenna 11 is suitable for receiving transmissions in a range used by communication satellites, for example L-band (1 to 2 GHz), S-band (2 to 4 GHz), C-band (4 to 8 GHz) , X band (from 8 to 12 GHz), Ku band (from 12 to 18 GHz), and Ka band (from 26.5 to 40 GHz). The antenna 11 may be suitable for receiving electromagnetic energy with any type of polarization (for example, linear, vertical, horizontal, elliptical and circular) or only some type of polarization. Furthermore, the reception pattern is directed towards the Earth when the observation satellite 10 is correctly positioned, that is, the observation satellite 10 orbits the Earth in a stable manner.

In addition, the control unit 12 may obtain information about the modulation scheme of the received electromagnetic energy (for example, phase shift keying, quadrature amplitude modulation, time division multiple access, code division multiple access, etc.). frequency division multiple access).

For communications between the observation satellite 10 and the ground, including command bearer, telemetry and data download link, one of the following techniques may be used, for example:

(a) Downlinking the data by using specific dedicated microwave frequencies. Normally the data downlink frequencies are different from those normally used by communications satellites 30 being analyzed in order to avoid causing interference.

(b) Performing a data downlink using an RF transmitter capable of dynamically adjusting its transmission frequency band to avoid interference to nearby satellites as the observation satellite 10 moves. This could be a pre-planned or stand-alone sequence.

(c) Transmission using low level spread spectrum. Use a spectrum that is already (or not) in use and transmit a very low level signal. The data rate is greatly reduced for each MHz, but results in a negative carrier to noise (C/N) ratio and therefore has minimal effect on any traffic being transmitted on the same frequencies.

(d) An optical canal. In this case, more than one ground station 20 may be needed to ensure stable downlink communication since clouds and other weather events may disrupt the optical link.

(e) A store-and-forward method, using any of the above methods but storing data from other parts of the orbit and then downlinking to a different part of the orbit (for example, could be achieved at a location with shorter intervals frequency already in use and high data transmission rate).

About the downlink communication from the observation satellite 10, any of the above methods can be used by:

(1) 'Wide' area transmission, covering part or all of the Earth from the vantage point of the satellite.

(2) On-board small beam tracking antennas that track multiple ground stations thereby maximizing power/throughput as well as simplifying coordination and enhancing data security.

(3) A transmission link to another satellite that acts as a data transmission.

The third alternative is schematically illustrated in Figure 10. Observation satellite 10 uses transmission satellite 31 to send a downlink transmission to ground station 20. More specifically, observing satellite 10 transmits to satellite 31. Transmitting satellite 31 then transmits the transmission to ground station 20, possibly after some processing.

Figure 8 schematically illustrates the composition of an observation satellite 10 in an embodiment of the present invention. In this embodiment, the observation satellite 10 receives electromagnetic energy in the C and Ku band using a phased array antenna 11. The received electromagnetic energy is then converted to a common frequency suitable for the digital signal processor. An A/D converter 121 digitizes the analog signal. A fast Fourier transform procedure is performed on the signal from A/D converter 121 in an FFT unit 122. A processing unit 123 may further process the output of the FFT unit 122 before it is stored in a buffer 131. The buffered data is transmitted to a ground station 20 via a downlink antenna 132 .

However, the invention is not limited to the exemplary implementation illustrated by Figure 8. Figure 8 illustrates a simple implementation and only serves to exemplify a functional hardware configuration for one approach. Many other possible implementations can be used.

Space based geolocation

Space-based geolocation means determining a location on the Earth's surface by means of an object in space. To do this, many possible radio direction finding (DF) techniques are possible. One possible mechanical implementation may involve, for example, rotating the spacecraft until the transmit signal is at its maximum intensity, such that the orientation of the spacecraft is parallel to the vector of the transmitted signal. More sophisticated approaches have more complex electronic and/or mechanical steps. Some additional approaches are described below.

From the natural vantage point in space, the observation satellite 10 can observe and monitor almost all uplink transmissions to geostationary satellites and collect relevant information on the directivity of uplink signals. The directivity of incoming uplink signals to a geostationary satellite is normally difficult to determine from the ground after the signal has been received and retransmitted by a communications satellite.

In orbit, determination of uplink locations can be achieved more directly compared to ground-based geolocation by directly solving for the incident angle of the transmission relative to the spacecraft and, given the altitude and position of the spacecraft, by therefore, the location on the surface of the Earth. This approach has significant advantages over the ground-based approach because it is not subject to the limitation of relying on external data sources and is a more robust determination method since it directly measures the uplink energy, rather than relying on a frequency and temporal Doppler shift from downlink signals from adjacent satellites. This space-based geolocation capability provides for the location of unauthorized uplink locations transmitting to a spacecraft causing interference to contracted traffic and contaminating spacecraft capacity.

Space-based geolocation can be performed with a multitude of techniques and hardware solutions. For example, four main technique classifications can be considered, namely: (T1) Radio Direction Finding (DF) which uses 'nullification' of uplink sources by means of a flexible or steerable antenna pattern, (T2) Frequency of Arrival (FoA) o Doppler analysis examining the frequency shift or frequency shift of an incident signal, (T3) angle of arrival (AoA) analysis comparing the received signal (phase, amplitude, etc.) between two or more antenna elements, and ( T4) Spectral estimation by correlation of collision signals on elements in a multi-element array.

(T1) FD techniques generally use the gain characteristics of an antenna to determine a collision signal delay. By varying the gain of an antenna in a given direction, through either mechanical movement or electrical means, the characteristics of a transmitted signal as received by the antenna may also vary, thus providing some understanding. the nature of the source of the transmitted signal. Variation of gain in a given direction could be achieved, for example, by relative movement of the antenna with respect to the source of a transmitted signal by means of gimbal or natural motion, or by dynamic variation of the gain pattern of an antenna. antenna by means of an array of electrically steerable antennas. DF techniques are mature and many hardware implementations have been created to apply these techniques for various applications.

In one case, FD techniques could be applied for space-based geolocation of uplink transmissions by equipping an observation satellite 10 with an antenna or antennas with a high gain slope characteristic and covering a portion of the surface of the satellite. the Earth as observed by the observation satellite 10. At any given point in the orbit, the antenna patterns of the observing satellite 10 could mechanically or physically move around the Earth's surface to 'search' for the interfering carrier. This movement could be deliberately controlled or could be processed in a repeating pattern to provide coverage of the entire Earth. Continuous monitoring of signal levels compared to a reference level as the pattern moves provides accurate measurements as the footprint moves closer to and further away from the target signal. With sufficient knowledge of the antenna patterns themselves, the movement of antenna patterns and the altitude of the spacecraft, the vector to the source of the interfering signal can be determined and the origin at the Earth's surface calculated. Since this technique relies on a direct energy measurement (rather measurement of lack of power while transmitter entering or exiting a 'null' pattern), such a system would be robust and would apply to a wide range of uplink signals.

Among the most flexible hardware solutions is using active phased arrays to electronically steer the footprint pattern on the Earth's surface. This has the advantage that there is no mechanically moving part, and it is adaptable to perform various types of search functions (repetition pattern, dedicated search, etc.). Other types of hardware implementations for the proposed third technique as described above include small spot beam antennas or antenna arrays that are mechanically moved or rotated on board the spacecraft, or fixed antennas or antenna arrays with nutation of the spacecraft in pitch, roll, yaw, or some combination thereof.

(T2) Frequency of arrival or Doppler analysis could also be used to perform space-based geolocation. Due to a relative motion between the observing satellite 10 and a transmitting station 50, the frequency of the signal received at an antenna on the observing satellite 10 may shift to the true frequency as transmitted by the transmitting station 50. Furthermore, due to the orbital geometry the rate of change of the induced Doppler shift can also be changed. By comparing the frequency offset to a known reference, or by comparing the frequency offset between two elements on board the spacecraft, or by analyzing the rate of change of the frequency offset as measured by the observing satellite, an understanding of possible source locations on the Earth's surface. The frequency shift can be particularly significant to observe due to the high relative speed of the observing satellite 10 in a retrograde orbit.

To perform this methodology, the observation satellite 10 requires at least one receiving antenna, but may have more than one. Since this approach relies heavily on frequency analysis of the transmitted signal, there are few requirements on the patterns, gain, and steering capability of the onboard antenna. Furthermore, it is worth noting that this technique for space-based geolocation relies on a stable transmit frequency or known variations in the transmit frequency such that variations in the actual frequency are not perceived as Doppler shifts due to relative motion.

(T3) Space-based geolocation by angle-of-arrival analysis could use a plurality of spacecraft-borne antennas with overlapping antenna patterns on the Earth's surface. Reference measurements between two antenna elements, as a simple example, can be a way to obtain basic information about the angle of arrival of a signal. Two antennas are considered, with overlapping but not identical reception patterns, so that the same signal received by the two antennas is received differently and at a different power level. By knowing the reception characteristics of both antenna elements, a rough understanding of the possible direction of arrival can be determined because only a small portion of possible direction vectors would result in the observed signals for both antennas. This method can be redefined and improved with more complex antennas and more of them to a usable degree.

By measuring the amplitude and/or (more usually) the phase of a given signal by one or more of the elements and comparing the differential relative to each other or to a reference measurement, an understanding of the incident angle of the source on the source can be determined. antenna and the origin of the transmission sources can be derived. In this case, high gain, high slope and low ramp-down performance of the antenna functions are advantageous to achieve high resolution and measurement accuracy. The technique is relatively simple to implement and can provide robust measurements for a wide range of uplink signal types.

(T4) Spectral estimation techniques rely on measuring signal sources impinging on an observation satellite 10 by multiple elements in an array. As a result, direction-of-arrival spectral estimation techniques require multiple antenna elements configured in a sophisticated array aboard an observation satellite 10 and pointed toward Earth such that the antenna gain patterns overlap and the antenna elements they are spaced appropriately based on the desired signal of interest.

Measurements of the amplitude and phase of incident signals at a given frequency a on each element can be correlated to produce an estimate of the composition of the incident signals, namely the angle of incidence in the array. Many measurements can be taken sequentially to statistically improve the characterization of a signal through averaging. Mathematically intensive processing can further improve performance through the use of subspace methods, such as multiple signal classification (MUSIC). Although computationally expensive and require a sufficiently large array of antennas, some correlation approaches can provide high-fidelity estimates of the direction of arrival of a plurality of simultaneously incident signals. With sufficient knowledge of the antenna array and the orientation and position of the observation satellite 10, space-based geolocation can be performed as the origin of each incident signal on the Earth's surface can be derived.

The optimal solution may indeed incorporate multiple of the above techniques and indeed some techniques may be compatible to perform the analyzes using the same spacecraft hardware. The synthesis of the output of multiple techniques as well as sequential analysis synthesis as the observing satellite 10 moves and the incident angle of a given signal changes can produce superior performance.

With the exception of some Doppler shift measurements in the art (T2 or T3), it is worth noting that space-based geolocation does not depend on retrograde (high relative velocity) motion of the spacecraft; Rather, retrograde motion allows relatively fast response time and coverage to perform space-based geolocation for each forward-orbiting satellite at a given altitude.

In one embodiment, which extends the concept of cooperation between a plurality of satellites in one direction as illustrated in Figure 10, a fractional spacecraft or multiple spacecraft working in tandem is used. For example, in one embodiment, a system involving a plurality of observation satellites is used. This may allow the use of smaller spacecraft that each have at least one antenna element that takes measurements simultaneously at some distance, and then communicates those signals to the larger spacecraft. The space vehicle can also be dimensioned identically. It may be advantageous to perform space-based geolocation to have antennas that are spaced very far apart (ie synthetic aperture interferometry) and do not have to be on the same spacecraft.

Ground-based geolocation with an observation satellite

In one embodiment, traditional ground-based time difference of arrival (TDOA) processing or frequency difference of arrival (FDOA) processing is used as a geolocation technique involving the observing satellite(s). Specifically, the observation satellite acts as a secondary satellite for the target satellite for TDOA-FDOA measurements or two observation satellites can be used in close proximity to perform ground-based TDOA-FDOA analysis of the signals. This involves transmitting the data corresponding to the aforementioned cases (i), (ii) or (iii), or any combination thereof (that is, as explained above, at least part of the received electromagnetic energy or information representing, or derived from, at least part of the electromagnetic energy received) to earth from the observing satellite(s).

This technique is identical to existing ground-based geolocation techniques, except that the technique involves one or more observation satellites in retrograde orbits that are specifically intended to assist in signal analysis and determination of the origin of uplink signals. In this sense, the technique may also be referred to as “ground-based, space-based geolocation”.

System Composition

In addition to the observation satellite 10, a system in one embodiment of the invention may include ground-based infrastructure and communications for transmitting processed data to the ground. Several ground stations 20 around the Earth with tracking antennas would perform telemetry, tracking and communication (TT&C) functions as well as receive data transmitted from an observation satellite 10 . The horizon-to-horizon time for observation satellite 10 at an altitude near geostationary orbit is approximately four hours, which is within a reasonable speed for existing antenna systems. At least three or four ground stations 20 are required to maintain constant communication with the observation satellite 10. In addition to traditional spacecraft command and control, ground stations 20 also send any necessary payload commands or queries to observation satellite 10, directing detection operations to produce specific measurements as desired by users.

The data downloaded by the observation satellite 10 can be large, and the data storage and reception chain on the ground is appropriately sized to handle a continuous stream of data from the observation satellite 10 through a demodulation and reception chain. traditional decryption. The data may be stored in one or more processing stations 40, fed from each ground station 20 sequentially as the receiving area of the satellite changes. Depending on the on-board processing implementation and the geolocation technique employed, an additional layer of processing would be performed in a centralized data center in order to produce the desired output and data format. The front end interfaces may allow users to direct payload commands to observation satellite 10 via ground stations 20 as well as allow access to received and processed data.

A processing station 40 in one embodiment of the invention is schematically illustrated in Figure 9. As shown in Figure 4, the processing station 40 is located on Earth. However, as explained above, since some processing may additionally or alternatively be performed within the observation satellite 10, or within another satellite, the same functions and/or units may also be incorporated, to the extent that this is necessary. , within the observation satellite 10, or within another satellite.

The processing station 40 comprises a processing unit 41, a memory unit 42 coupled to the processing unit 41, and a communication unit 43 coupled to the processing unit 41.

Processing unit 41 may include a processor, microprocessor, or processing logic that can interpret and execute instructions, such as those described hereinabove (eg with reference to Figure 11). These operations may be performed in response to the processing unit 41 executing software instructions contained in a computer readable medium, such as a memory unit 42. Software instructions contained in memory unit 42 may cause processing unit 41 to perform operations or procedures described herein. Alternatively, hardwired circuitry may be used instead of or in combination with software instructions to implement procedures and/or operations described herein. Therefore, the implementations described herein are not limited to any specific combination of hardware and software.

Memory unit 42 is configured to store transmissions from one or more observation satellites 10 . Memory unit 42 may include a RAM or other type of dynamic storage device that can store information and instructions for execution processing unit 41 . Memory unit 42 may also include a ROM device or other type of static storage device that can store static information and instructions for using processing unit 41 . Memory unit 42 may also include magnetic and/or optical recording media and a corresponding hard disk drive.

The communication unit 43 is configured to communicate with one or more stations 20 on the ground. The communication unit 43 may include any transceiver-like mechanism that allows a processing station 40 to communicate with other devices and/or systems.

The memory unit 42 may store a computer program that can be loaded into the processing unit 41 comprising code for executing the steps of the described method embodiments according to the present invention. Although not illustrated/for conciseness, a bus, including a path that enables communication between components of the processing station 40, an input device, including a mechanism that allows an operator to input information to a processing station 40, such as a keypad, keyboard, mouse, pen, voice recognition and/or biometric mechanisms, etc., and an output device, including a mechanism that broadcasts information to the operator, such as a screen, a printer, a loudspeaker, etc.

Fig. 11 is a flowchart of a method performed by the system in one embodiment. In step S11, at least one ground station 20 obtains a signal originating from an orbiting observation satellite 10 having an inclination greater than 90° and less than 270° (i.e. in a retrograde orbit), and communicating at least one of: (i) electromagnetic energy received by the satellite, information representing (ii) electromagnetic energy received by the satellite, and (iii) information that is derived from electromagnetic energy received by the satellite.

Information representing the received electromagnetic energy may be produced in the observation satellite 10 by digitizing and compressing the received electromagnetic energy. In the latter alternative, information that is derived from the received electromagnetic energy may be produced at the observation satellite 10 by determining the location (eg, longitude and altitude) of the source of the received electromagnetic energy.

In step S12, at least one processing station 40 estimates from the received electromagnetic energy or the information representing, or derived from, the received electromagnetic energy, obtained by the at least one ground station, at least one of: (a) the composition of at least part of the received electromagnetic energy; (b) a location on Earth of the origin of at least some of the received electromagnetic energy; (c) a level of received electromagnetic energy that reaches at least part of the geostationary orbit; and (d) at least one characteristic of an uplink transmission. In one embodiment, ground station 20 and processing station 40 may be collocated or form a single station.

The composition of at least part of the received electromagnetic energy may comprise the energy spectrum or polarization of the received electromagnetic energy. The location on Earth of the origin of at least part of the received electromagnetic energy may comprise the longitude and latitude of the origin. The received electromagnetic energy level reaching at least part of the geostationary orbit is useful in determining an interference map of the geostationary orbit. A characteristic of an uplink transmission may comprise the modulation scheme of the uplink transmission.

Figure 12 is a flowchart of a method performed by a system in an embodiment of the invention.

In steps S21 and S22, immediate or preloaded configuration commands are executed and the satellite configuration is loaded. In step S23, the satellite receives uplink electromagnetic energy. Uplink electromagnetic energy may include, for example, energy destined for other satellites. In step S24, the received electromagnetic energy is subjected to frequency conversion or frequency translation. Additional steps may include analog-to-digital conversion, digital processing of received electromagnetic energy, data reduction or merging of multiple data sources, digital-to-analog conversion, frequency translation, etc.

In step S25, at least part of the received electromagnetic energy is transmitted (eg to a ground station on Earth). The received electromagnetic energy is digitized in step s 26 and digitally processed in step S27. The processing may include using known processing functions such as fast Fourier transform, Doppler shift analysis, rate Doppler analysis, direction of arrival or angle of arrival processing, time difference of arrival processing, frequency difference processing of arrival, and/or reference comparison of power, frequency, phase between two or more receiving elements or instances in time.

The output of step S27 can be used for various processing steps. In step S28, the processed data may be synthesized with external sources such as the characteristics and origin of reference signals, orbital position, velocity data and orientation of the satellite. The synthesized data can then be used in coordinate transformation and projection of an approximate location on the Earth's surface in step S29. Thereby, the location of a transmitter can be estimated in step S30 (geolocation). Alternatively or additionally, the synthesized data may be synthesized using multiple analyzes over time in step S31. Thereby, antenna characterizations, conformance measurements, or spectral environment trending can be obtained at step S32.

Furthermore, the output of step S27 may be further processed by demodulating the electromagnetic energy received in step S33. Thereby, it becomes possible to perform carrier signal analysis (step S34).

In further embodiments of the invention, any one of the procedures, steps or processes described above may be implemented using computer-executable instructions, for example in the form of computer-executable procedures, methods or the like, in any type of computer language, and/or or in the form of software included in firmware, integrated circuits or the like.

Although the present invention has been described based on detailed examples, the detailed examples serve only to provide a person skilled in the art with a better understanding, and are not intended to limit the scope of the invention. The scope of the invention is further defined by the appended claims.

In any one of the above embodiments, the observation satellite may also comprise an additional receiving antenna having a receiving pattern directed away from the Earth, the antenna being suitable for receiving electromagnetic energy in the radio frequency range. In such a way, it is possible for the observation satellite to receive a given signal that is fed to a given target satellite (which orbits at a higher altitude than the orbit in which the observation satellite orbits), as well as the repeated given signal that is emitted by the target satellite. For example, the target satellite may be orbiting in a geostationary orbit, in which case the observation satellite's additional receiving antenna may be oriented at or near the zenith direction, provided that the observation satellite orbits at a lower altitude than the orbit. geostationary. The advantage of this approach is that it allows the input and output signals to be used together to cancel out some sources of error (any slight frequency drift of the given signal, for example, that would otherwise result in geolocation solution errors) and allows characterization of the performance of the target satellite itself.

Claims (19)

i. Satellite (10) to obtain information on electromagnetic energy emitted from a source (50) on Earth, or from sources on Earth, the satellite (10) orbiting the Earth in an orbit having an inclination greater than 90° and less than 270°; and comprising the satellite (10): at least two reception antennas (11), each of the at least two reception antennas (11) has a reception pattern directed towards the Earth, and is suitable for receiving electromagnetic energy in a radio frequency range as the satellite (10) is orbiting with respect to the Earth's surface, and the at least two receiving antennas (11) forming overlapping but not identical receiving patterns; Y a transmitter configured for at least one of the following three operations: retransmit at least part of the received electromagnetic energy; transmit information representing at least part of the received electromagnetic energy; and transmitting information that is derived from at least part of the received electromagnetic energy. 2. Satellite (10) to obtain information on electromagnetic energy emitted from a source on Earth, or from sources on Earth, the satellite (10) orbiting the Earth in an orbit having an inclination greater than 90° and less than 270°; and comprising the satellite (10): at least two receiving antennas (11), at least one of which has a reception pattern directed toward Earth, and is suitable for receiving electromagnetic energy in a radio frequency range as the satellite (10) is orbiting with respect to the Earth's surface, and at least one other of which has a reception pattern directed away from Earth, and is suitable for receiving electromagnetic energy in a radio frequency range as the satellite (10) is orbiting with respect to the Earth's surface, and a transmitter configured for at least one of the following three operations: retransmit at least part of the received electromagnetic energy; transmit information representing at least part of the received electromagnetic energy; and transmitting information that is derived from at least part of the received electromagnetic energy. Satellite (10) according to claim 1 or 2, which is suitable for obtaining information on electromagnetic energy emitted from a source on Earth, or from sources on Earth, the electromagnetic energy reaching the geostationary orbit. 4. Satellite (10) according to any one of the preceding claims, in which the transmitter is configured to transmit, towards Earth, at least part of the electromagnetic energy received, or the information that represents, or is derived from, the least part of the received electromagnetic energy. 5. Satellite (10) according to any one of the preceding claims, in which the information derived from at least part of the received electromagnetic energy is obtained by processing at least part of the energy electromagnetic field received inside the satellite (10). Satellite (10) according to claim 5, in which the processing comprises at least one of the following eleven operations: selectable down-conversion of an analog signal to a common intermediate frequency; analog to digital conversion of signals provided by at least part of the received electromagnetic energy; spectrum analysis of at least part of the received electromagnetic energy; Doppler shift analysis of at least part of the received electromagnetic energy; Doppler rate analysis of at least part of the received electromagnetic energy; processing direction of arrival or angle of arrival; time difference of arrival (TDOA) processing; frequency difference of arrival (FDOA) processing; reference measurements between two or more antenna elements; data filtering; Y data compression. Satellite (10) according to any one of the preceding claims, in which the at least two receiving antennas (11) are suitable for receiving electromagnetic energy in a radio frequency range between 1 GHz and 100 GHz, preferably in a radio frequency range which is at least one of the following six intervals: between 1 and 2 GHz; between 2 and 4 GHz; between 4 and 8GHz; between 8 and 12 GHz; between 12 and 18 GHz; Y between 26.5 and 40 GHz. Satellite (10) according to any one of the preceding claims, in which at least one of the following two paragraphs applies: the at least two receiving antennas (11) are suitable for receiving electromagnetic energy in a radio frequency range used by geostationary satellites to receive, or send, signals from, or to, the Earth, and the received electromagnetic energy, received by each reception antenna (11) having a reception pattern directed towards the Earth, comprises energy intended for at least one other satellite (30). Satellite (10) according to any one of the preceding claims, in which the at least two receiving antennas (11) are suitable for receiving electromagnetic energy having at least one of the following five polarizations: a linear polarization; a vertical polarization; a horizontal polarization; an elliptical polarization; Y a circular polarization. Satellite (10) according to any one of the preceding claims, in which each receiving antenna (11) having a receiving pattern directed towards the Earth is configured to receive, during an orbital period, electromagnetic energy from an area that It covers more than half of the Earth's surface. Satellite (10) according to any one of the preceding claims, in which the received electromagnetic energy, received by each reception antenna (11) having a reception pattern directed towards the Earth, comprises more than just information intended to control the satellite itself (10). Satellite (10) according to any one of the preceding claims, wherein the satellite (10) orbits the Earth in an orbit having an inclination greater than 175° and less than 185°. Satellite (10) according to any one of the preceding claims, in which the satellite (10) orbits the Earth in an orbit having an apogee that differs by no more than 4000 kilometers from the geostationary orbit, and preferably in which The satellite (10) orbits the Earth in an orbit having an apogee that is at an altitude in either of the following two intervals: between 31,700 and 34,700 kilometers above mean sea level; Y between 36,700 and 39,700 kilometers above mean sea level. Satellite (10) according to any one of the preceding claims, wherein the satellite (10) orbits the Earth in an orbit having an eccentricity that is less than 0.05. Satellite (10) according to any one of the preceding claims, wherein the satellite (10) is not itself a communication satellite for transmitting end-user information from one point on Earth to another point on Earth. 16. Satellite (10) according to any one of the preceding claims, wherein the transmitter is configured to transmit at least part of the received electromagnetic energy or information representing, or derived from, at least part of the electromagnetic energy received using at least one of the following five operations or means: (a) performing a downlink using specific dedicated microwave frequencies; (b) performing a downlink using a transmitter that can dynamically adjust its transmission frequency band; (c) low level spread spectrum; (d) at least one optical communication link; Y (e) a store and forward method. 17. Satellite (10) according to any one of the preceding claims, wherein the satellite (10) further comprises a receiver connected to at least one receiving antenna (11), the receiver being reconfigurable to different frequencies in a range of the radio frequency spectrum. 18. System for obtaining information on electromagnetic energy emitted from a source (50) on Earth, or from sources on Earth, said system comprising at least two satellites (10) according to any one of the preceding claims. 19. System for obtaining information on electromagnetic energy, said system comprising: at least one satellite (10) according to any one of claims 1 to 17, at least one ground station (20) configured to obtaining, from the at least one satellite (10), the received electromagnetic energy or the information that represents, or is derived from, the received electromagnetic energy, and at least one processing station (40) configured to estimate, from received electromagnetic energy or information representing, or derived from, received electromagnetic energy, obtained by the at least one ground station (20), at least one of: the composition of at least part of the received electromagnetic energy; a location on Earth of the origin of at least some of the received electromagnetic energy; a level of received electromagnetic energy that reaches at least part of the geostationary orbit; Y at least one characteristic of an uplink transmission. Method performed by a system to obtain information on electromagnetic energy, said method comprising the steps of: obtain (S11), by means of at least one station (20) on the ground, a signal originating from a satellite (10) orbiting the Earth in an orbit having an inclination greater than 90° and less than 270°, the satellite (10) having at least two receiving antennas (1 l), each one of which has a reception pattern directed towards the Earth, and the at least two reception antennas (11) forming overlapping but not identical reception patterns, and communicate at least one of the following three elements: electromagnetic energy received by the satellite (10), information representing electromagnetic energy received by the satellite (10), and information derived from electromagnetic energy received by the satellite (10), and estimating (S12), by means of at least one processing station (40), from at least part of the received electromagnetic energy or the information that represents, or is derived from, at least part of the received electromagnetic energy, obtained by the at least one ground station (20), at least one of: the composition of at least part of the received electromagnetic energy; a location on Earth of the origin of at least some of the received electromagnetic energy; a level of received electromagnetic energy that reaches at least part of the geostationary orbit; and at least one characteristic of an uplink transmission. Method performed by a system to obtain information on electromagnetic energy, said method comprising the steps of: obtain (S11), by means of at least one station (20) on the ground, a signal originating from a satellite (10) orbiting the Earth in an orbit having an inclination greater than 90° and less than 270°, the satellite (10) having at least two receiving antennas (11), at least one of which has a reception pattern directed toward Earth, and at least one other of which has a reception pattern directed away from Earth, and communicate at least one of the following three elements: electromagnetic energy received by the satellite (10), information representing electromagnetic energy received by the satellite (10), and information derived from electromagnetic energy received by the satellite (10), and estimating (S12), by means of at least one processing station (40), from at least part of the received electromagnetic energy or the information that represents, or is derived from, at least part of the received electromagnetic energy, obtained by the at least one station (20) on land, at least one of: the composition of at least part of the received electromagnetic energy; a location on Earth of the origin of at least some of the received electromagnetic energy; a level of received electromagnetic energy that reaches at least part of the geostationary orbit; and at least one characteristic of an uplink transmission. Method according to claim 20 or 21, wherein estimating the location comprises estimating a longitude and latitude. Method according to any one of claims 20 to 22, wherein estimating a location on Earth of the origin of at least part of the received electromagnetic energy comprises estimating the location of a source of interference. Method according to any one of claims 20 to 23, wherein estimating at least one characteristic of an uplink transmission comprises estimating an uplink pattern of at least one of an antenna on Earth; Y a group of antennas on Earth. Use of a satellite (10) according to any one of claims 1 to 17, or information obtained from a satellite (10) according to any one of claims 1 to 17, or a system according to claim 19, to estimate at least one of: the composition of at least part of the received electromagnetic energy; a location on Earth of the origin of at least some of the received electromagnetic energy; a level of received electromagnetic energy that reaches at least part of the geostationary orbit; and at least one characteristic of an uplink transmission.